Expansible chamber motors using pressurized air or hydraulic oil commonly utilize cushioning structure to prevent deleterious impact of the piston components with the motor heads at the termination of a stroke. Such cushion structure usually includes a passage defined in a motor head, usually concentric with the cylinder, through which exhausted medium passes. This exhaust passage receives a valve member affixed to piston structure as the piston approaches the head wherein the valve member restricts the flow of exhaust medium through the passage slowing the rate of flow of the exhausting medium and utilizing such medium for cushioning purposes at the termination of the piston stroke.
Such cushioning apparatus normally utilizes an annular seal within the passage opening which cooperates with the piston mounted valve member to seal the valve member with respect to the passage during the cushioning phase. Bleed means having a regulatable restricted flow communicate with the cylinder chamber adjacent the head allowing the cushioning medium to be exhausted at a controlled rate thereby permitting the piston to move through its full stroke, yet at a reduced velocity, to control the engagement between the piston components and the motor head.
When pressurizing the chamber, the pressurized medium is imposed upon the cushioning apparatus, and it is known to construct the passage seal ring in such a manner that medium flow about the seal is permitted to pressurize the adjacent motor chamber, and initiate piston movement. Various seal configurations have been utilized to improve the operating and life expectancy of cushion seal apparatus, including seal rings, and typical cushioned expansible motor constructions are shown in the assignee's U.S. Pat. Nos. 2,719,510 and 2,804,052 and in U.S. Pat. Nos. 2,704,996; 2,710,595; 2,755,775; 2,853,974; 3,267,815; 3,626,807; 3,805,672 and 4,088,061.
Presently available cushioning apparatus of the aforementioned type often impose friction upon the piston structure which increases the pressure required to initiate piston movement, and such seals are often of the lip seal type which necessitates that the pressurized medium be sufficient to raise the lip seal before significant flow through the seal is possible. Also, known cushioning apparatus is relatively expensive to manufacture, and is not of such a concise configuration as to readily permit the associated motor head to accommodate bleed off structure. Further, the installation of cushion structure of the known type into expansible chamber motors is relatively complex and time consuming, and if the assembly is not properly achieved failure of the cushion structure will readily occur.
It is an object of the invention to provide cushion seal structure for an expansible chamber motor wherein the seal has improved friction reducing characteristics and permits pressurized medium to bypass the seal at lower pressures than usual.
A further object of the invention is to provide a cushion seal for an expansible chamber motor wherein the seal results in a shorter cycle time lag during operation and the seal may be readily assembled into a permanent groove within the motor head and is maintained therein by the normal configuration of the seal.
An additional object of the invention is to provide a cushion seal for an expansible chamber motor which is formed of a synthetic plastic material, is economical to manufacture and has a long effective operating life, and is capable of permitting relatively high medium flow rates to circumvent the seal during pressurization of the adjacent cylinder chamber.
In the practice of the invention the head of an expansible chamber motor includes a concentric fluid passage through which pressurized medium enters the associated cylinder chamber, and is exhausted therefrom. An annular groove defined in this passage receives a synthetic plastic cushion seal, such as formed of urethane, and the seal includes an inner bore generally of conical configuration which cooperates with a cylindrical valve member mounted upon the piston structure which enters the passage as the piston approaches the cylinder head.
The seal includes a radial face adapted to engage and seal against the passage groove during exhausting of the pressurized medium, and bleed passages formed in the head permit the pressurized medium which has produced a cushioning effect to be bled from the cylinder at a controlled rate.
When pressurized medium is to be introduced into the adjacent cylinder chamber, the cushion seal permits medium flow therearound due to axial displacement of the seal ring which disengages the seal ring radial surface from the passage groove face. Axial channels defined in the seal circumference communicate with radial channels defined in the seal face nearest the piston wherein the channels are capable of handling a relatively large capacity flow of pressurized medium to initiate piston movement facilitating withdrawal of the valve from the head passage.
The bore of the seal is of a conical-cylindrical configuration wherein a limited area of engagement exists between the seal and valve and the characteristics of the seal are such as to minimize frictional drag between the seal and valve components, and minimize the frictional resistance of pressurized medium flowing therearound.
The flexible and resilient characteristics of the seal permits the seal to be readily deformed for assembly purposes into the motor head, yet the seal configuration, and the associated head groove, prevent "roll out" of the seal from the groove due to frictional or pressure forces thereon.